Memories can be turn on by stimulating brain cells: Study

Washington: Imagine recalling those favourite old memories with just the flip of a switch. Well, scientists at MIT claim it is possible to activate a memory on demand by stimulating only a few neurons of your brain with light.

The technique, called optogenetics, is a powerful medium that shows memories reside in specific cells in the brain and that they can be turned on, they said.

The research, conducted on mice and published in journal Nature, gives scientists a way to explore myriad questions -- how memories are preserved and recalled, and how they can erode over time, LiveScience reported.

"We demonstrate that behaviour based on high-level cognition, such as the expression of a specific memory, can be generated in a mammal by highly specific physical activation
of a specific small subpopulation of brain cells, in this case by light," said lead study author Susumu Tonegawa, the Picower Professor of Biology and Neuroscience at MIT.

To artificially turn on a memory, the researchers first set out to identify the neurons that are activated when a mouse is making a new memory.

To accomplish this, they focused on a part of the brain called the hippocampus, known for its role in learning and memory, especially for discriminating places. Then they
inserted a gene that codes for a light-sensitive protein into hippocampal neurons, enabling them to use light to control the neurons.

With the light-sensitive proteins in place, the team gave the mouse a new memory. They put the animal in an environment where it received a mild foot shock, eliciting the normal fear behavior in mice: freezing in place. The mouse learned to associate a particular environment with the shock.

Next, the team attempted to find out whether they could artificially activate the fear memory. They directed light on the hippocampus, activating a portion of the neurons involved in the memory, and the animals showed a clear freezing response.

Stimulating the neurons appears to have triggered the entire memory, the researchers said.

The researchers performed several key tests to confirm that it was really the original memory recalled. They tested the mice with the same light-sensitive protein but without the shock; they tested mice without the light-sensitive protein; and they tested mice in a different environment not associated with fear.

None of these tests yielded the freezing response, reinforcing the conclusion that the pulse of light indeed activated the old fear memory.

The study shows that it`s possible to artificially stimulate a few neurons to activate an old memory, controlling an animals` behaviour without any sensory input, the researchers said.

This is significant because it provides a new approach to understand how complex memories are formed in the first place. In 2010, optogenetics was named the scientific Method of the Year by the journal Nature Methods. The technology was introduced in 2004 by a research group at Stanford University led by Karl Deisseroth, a collaborator on this research.

Over the last several years, optogenetics has provided powerful insights into the neural underpinnings of brain disorders like depression, Parkinson`s disease, anxiety, and
schizophrenia.